In his classic work Masaaki Hatsumi reveals the hidden secrets and truths about this mysterious and fascinating Japanese martial art. He looks at the traditions, training, and techniques, then shows how this knowledge will lead readers to an understanding of two essential principles: that ninjutsu is the very foundation of the martial arts; and that ninjutsu illuminates its true spiritual significance. Now in paperback, the book features detailed demonstration photos, sidebars on many topics related to ninjutsu, and new material by Hatsumi explaining the relevance of ninjutsu in today's world.